Flexible packaging film is produced in great volume to meet extensive demand in a variety of industrial applications in which such films are utilized. The hallmarks of good flexible multilayer packaging films are superior interlayer adhesion, toughness, optical, and safety properties and low cost at the lowest possible gauge. To date, no single class of packaging film is optimum in all of these categories. For example, although flexible polyvinyl chloride (PVC) can be fabricated into a tough, clear and low cost packaging film product, the safety aspect of flexible PVC film, especially in the packaging of edible material, is suspect. There is thus a long felt need in the art for a packaging film, free of vinyl chloride, which provides the advantages associated with flexible PVC film.
Polyolefinic film is environmentally safe. In addition, various polyolefinic films are quite clear and relatively inexpensive. However, the problem associated with the use of polyolefin films, which are highly attractive from the point of view of environmental safety, is their low degree of toughness compared to flexible PVC film. For example, one of the strongest of the polyolefinic films is polypropylene (PP) film. Still, the toughness characteristics of PP film, as measured by dart impact or puncture resistance, are significantly below the corresponding values of less environmentally safe flexible PVC film.
It is well known in the art to laminate layers in order to increase toughness of thin films. However, this expedient cannot overcome the inherent low strength characteristics of polyolefins. This is due to one or more of the following deficiencies of multilayer polyolefin films: failure due to delamination, excessive thickness and loss of optical properties. For example, when laminated films are utilized to make packages that are heat sealed, one of the problems often encountered is that when an attempt is made to pull this package open, the film begins to delaminate (peel off in layers rather than allowing separation as if the film is one layer at the point of heat sealing). These defects emphasize that laminate films of polyolefin are unsuitable replacements for flexible PVC high strength films.
There is a strong need in the art for a new class of compatible polymers that can be bonded to polyolefin films to increase the toughness of the films without adversely affecting the desirable properties of polyolefin packaging films and allowing the design of a structure that meets, among others, desired permeation requirements.